Electrode structure for solid polymer type fuel cell

ABSTRACT

A water holding layer having a carbon-based material and a water holding material is arranged on an anode diffusion layer. The water holding material is contained at 5 to 20 wt % of total weight of the water holding material and an electron conductive material. Alternatively, carbon particles having water absorption amount at saturated water vapor pressure at 60° C. is not less than 150 cc/g are contained in the anode diffusion layer. Water absorption ratio of the anode diffusion layer at 60° C. is in a range of 40 to 85%, a differential pressure is in a range of 60 to 120 mmaq, and a ratio of quantity of electric charge of catalytic material of the cathode catalytic layer existing in proton conductive passage from the polymer electrolyte membrane is not less than 15% of the quantity of electric charge of all the catalytic material existing in the cathode catalytic layer. Furthermore, a layer including carbon particles having water absorption amount at saturated water vapor pressure at 60° C. of not less than 150 cc/g and fluorine resin, is arranged on a carbon-based material having a contact angle with water of not more than 90° by performing a hydrophilic treatment. The water absorption ratio at 60° C. is in a range of 40 to 85 wt %, and the penetration resistance is not more than 5 mΩ.

TECHNICAL FIELD

The present invention relates to a membrane electrode assembly forpolymer electrolyte fuel cells, and in particular, relates to a membraneelectrode assembly for polymer electrolyte fuel cell in which efficiencydeterioration when there is a shortage of fuel is reduced.

BACKGROUND ART

A unit of a polymer electrolyte fuel cell is formed by laminatingseparators at both sides of a tabular membrane electrode assembly (MEA),and then plural units are laminated to form a fuel cell stack. Themembrane electrode assembly is a layered structure in which a polymerelectrolyte membrane is arranged between a pair of gas diffusionelectrodes forming a cathode and an anode. The gas diffusion electrodeis a structure in which a gas diffusion layer is formed on an outersurface of an electrode catalytic layer contacting the electrolytemembrane. In such a fuel cell, hydrogen gas supplied through a gaspassage of the separator facing on the gas diffusion electrode of theanode and oxidizing gas supplied through a gas passage of the separatorfacing on the gas diffusion electrode of the cathode electrochemicallyreact and thereby generate electricity.

In an operation of the fuel cell, the gas diffusion layer conductselectrons generated by the electric chemical reaction between theelectrode catalytic layer and the separator, and at the same time,diffuses fuel gas and oxidizing gas. Protons (H⁺) and electrons aregenerated from the fuel gas in the anode electrode catalytic layer,water is generated from oxygen, protons, and electrons in the cathodeelectrode catalytic layer, and protons are ion conducted through theelectrolyte membrane. As a result, electric power can be obtainedbetween the electrode catalytic layers of cathode and anode.

During driving of vehicles or the like, power output sometimes variesgreatly. Therefore, in the case in which the above-mentioned polymerelectrolyte fuel cell is used as a power source, fuel gas cannot besupplied sufficiently to meet the required amount of fuel gas. In thiscase, fuel gas runs short temporarily in the membrane electrodeassembly. During the circumstance of fuel shortage, current ismaintained by using protons supplied from the electrolysis of watershown in following formula (1).2H₂O→4H⁺+4e ⁻+O₂  (1)

Furthermore, in the case in which the fuel shortage continues more inthe circumstances promoting the electrolysis of water, the followingcorrosion reaction of carbon (2) may occur.2H₂O+C→4H⁺+4e ⁻+CO₂  (2)

In the reaction (2), carbon black which is a support body of thecatalyst is corroded, and power generation efficiency of the membraneelectrode assembly is deteriorated.

To solve such a problem, a technique in which corrosion resistance ofcarbon is improved by increasing supported ratio of catalyst or by usingcarbon having higher corrosion resistance is disclosed in PatentApplication Publication No.01/15254). Furthermore, from the viewpoint ofthe above reaction of formula (1), a technique in which catalystpromoting electrolysis of water is added to the anode catalytic layer(Patent Application Publications No. 01/15247 and No. 01/15255), atechnique in which material to increase water amount is added to theanode catalytic layer or diffusion layer (Patent ApplicationPublications No. 01/15255 and No. 01/15249) or the like are disclosed.

The conventional techniques mentioned above are effective in a temporaryfuel shortage; however, in the case in which fuel shortage occursrepeatedly in practical operations or in the case of a rated operation,there is a problem of the flooding phenomenon. Flooding is a phenomenonin which micropores of gas diffusion flow passage in the anode catalyticlayer are filled with water, and therefore gas diffusion is inhibited.The flooding inhibits supply of fuel gas, enlarges the area of fuelshortage in the anode (fuel gas electrode), and promotes corrosionreaction of carbon, and as a result, deteriorates efficiency of themembrane electrode assembly.

DISCLOSURE OF THE INVENTION

The present invention was completed in view of the above-mentionedcircumstances. An object of the present invention is to provide amembrane electrode assembly for polymer electrolyte fuel cell in whichefficiency deterioration at shortage of fuel is restrained.

In the membrane electrode assembly for polymer electrolyte fuel cell ofthe present invention having a polymer electrolyte membrane, a cathodeand an anode both having catalytic layers and diffusion layers, theanode diffusion layer has characteristics (1) to (3) below.

-   (1) water holding layer which contains 5 to 20 wt % of water holding    material improving water holding property to the total amount of    electron conductive material and water holding material, is arranged    on carbon-based material, or carbon particles whose water absorption    amount at saturated water vapor pressure at 60° C. is not less than    150 cc/g is contained,-   (2) water absorption ratio of the anode diffusion layer at 60° C. is    in a range of 40 to 85%, and-   (3) differential pressure measured by a differential pressure    measuring method is in a range of 60 to 120 mmaq, and ratio of    quantity of electric charge of catalytic material of the cathode    catalytic layer existing in a proton conductive passage from the    polymer electrolyte membrane measured by a cyclic voltammetric    method is not less than 15% to the quantity of electric charge of    all the catalytic material existing in the cathode catalytic layer.

In the present invention, the anode catalytic layer does not have awater holding property; however, the water holding layer in which waterholding material is contained at 5 to 20 wt % to the total amount of theelectron conductive material and the water holding material, is arrangedon the carbon-based material, or alternatively, carbon particles havingwater absorption amount at saturated water vapor pressure at 60° C. isnot less than 150 cc/g, are contained. Therefore, water absorption ratioof the anode diffusion layer at 60° C. is in a range of 40 to 85%, andthe anode diffusion layer has high water holding property. In the casein which fuel runs short, water is supplied from the anode diffusionlayer to the anode catalytic layer, the water is electrolyzed in theanode catalytic layer, protons are supplied to the polymer electrolytemembrane.

In this way, in the membrane electrode assembly for polymer electrolytefuel cell of the present invention, since the water is supplied to theanode catalytic layer only at shortage of fuel, flooding does not occurin the anode catalytic layer, and on the other hand, since water iselectrolyzed in the anode catalytic layer during the shortage of fuel,corrosion reaction of carbon which is a next step of electrolysis ofwater can be restrained.

In a membrane electrode assembly for polymer electrolyte fuel cell ofanother preferred embodiment of the present invention, having a polymerelectrolyte membrane, and an anode and a cathode both having catalyticlayers and diffusion layers, the anode diffusion layer hascharacteristics (1) to (4) below.

-   (1) a layer having fluorine resin and carbon particles having water    absorption amount at saturated water vapor pressure at 60° C. of not    less than 150 cc/g, is arranged on a carbon-based material which is    processed to be hydrophilic and to have a contact angle with water    of not more than 90°,-   (2) water absorption ratio of the anode diffusion layer at 60° C. is    in a range of 40 to 85%,-   (3) penetration resistance measured by a penetration resistance    method is not more than 5 mΩ, and-   (4) differential pressure measured by a differential pressure    measuring method is in a range of 60 to 120 mmaq, and ratio of    quantity of electric charge of catalytic material of the cathode    catalytic layer existing in a proton conductive passage from the    polymer electrolyte membrane measured by a cyclic voltammetric    method is not less than 15% to the quantity of electric charge of    all the catalytic material existing in the cathode catalytic layer.

In this embodiment, the anode catalytic layer does not have a waterholding property; however, a carbon-based material of the anodediffusion layer is processed to be hydrophilic, and that carbonparticles having water absorption amount at saturated water vaporpressure at 60° C. of not less than 150 cc/g, are contained. Therefore,water absorption ratio of the anode diffusion layer at 60° C. is in arange of 40 to 85%, and the anode diffusion layer has high water holdingproperty. In the case in which fuel runs short, water is supplied fromthe anode diffusion layer to the anode catalytic layer, the water iselectrolyzed in the anode catalytic layer, and protons are supplied tothe polymer electrolyte membrane.

Furthermore, in a membrane electrode assembly for polymer electrolytefuel cell of another desirable embodiment of the present invention,having a polymer electrolyte membrane, and an anode and a cathode bothhaving catalytic layers and diffusion layers:

-   the catalytic layers have at least catalyst, carbon particles    supporting the catalyst, and polymer electrolyte;-   the cathode catalytic layer contains void forming agent;-   the diffusion layers have a layer containing carbon particles and    fluorine resin on carbon-based material;-   the carbon particles in the anode diffusion layer has water    absorption amount at saturated water vapor pressure at 60° C. of not    less than 150 cc/g;-   the carbon particles in the cathode diffusion layer has water    absorption amount at saturated water vapor pressure at 60° C. of not    more than 150 cc/g;-   water absorption ratio of the anode diffusion layer at 60° C. is in    a range of 40 to 85%,-   differential pressure of the anode diffusion layer and the cathode    diffusion layer measured by a differential pressure measuring method    is in a range of 60 to 120 mmaq;-   penetration resistance measured by a penetration resistance method    is not more than 5 mΩ; and-   ratio of quantity of electric charge of catalytic material of the    cathode catalytic layer existing in proton conductive passage from    the polymer electrolyte membrane measured by a cyclic voltammetric    method is not less than 15% to the quantity of electric charge of    all the catalytic material existing in the cathode catalytic layer.

In this embodiment, carbon particles having water absorption amount atsaturated water vapor pressure at 60° C. of not less than 150 cc/g, arecontained in the anode diffusion layer, carbon particles having waterabsorption amount at saturated water vapor pressure at 60° C. of notmore than 150 cc/g, are contained in the cathode diffusion layer, andwater absorption ratio of the anode diffusion layer at 60° C. is in arange of 40 to 85%. Therefore, amount of water of reverse diffusion fromthe cathode to the anode is increased, and water holding property of theanode diffusion layer is high. In the case in which fuel runs short,water is supplied from the anode diffusion layer to the anode catalyticlayer, the water is electrolyzed in the anode catalytic layer, protonsare supplied to the polymer electrolyte membrane.

Furthermore, in a membrane electrode assembly for polymer electrolytefuel cell of another desirable embodiment of the present invention,carbon-based material of the anode diffusion layer is processed to behydrophilic and to have a contact angle with water of not more than 90°,and carbon-based material of the cathode diffusion layer is processed tobe hydrophobic and to have a contact angle with water of not less than130°. In this embodiment, the anode diffusion layer can have high waterholding property, reverse diffusion of generated water and suppliedwater from the cathode to the anode can be performed efficiently,electrolysis of water in the anode catalytic layer can be promoted, andcorrosion reaction of carbon can be restrained more.

In the membrane electrode assembly for polymer electrolyte fuel cell ofthe present invention, since constituent elements except for the cathodecatalytic layer, cathode diffusion layer, and anode diffusion layer arenot limited in particular, these constituent elements are explainedbelow.

The anode diffusion layer of membrane electrode assembly for polymerelectrolyte fuel cell of the first and second embodiments of the presentinvention, can be consist of (1) carbon-based material, (2) a layercontaining carbon particles and fluorine resin arranged thereon, and (3)a layer containing carbon particles, polymer electrolyte, void formingagent, and water holding material further arranged thereon.Alternatively, it can be consist of (1) carbon-based material and (2) alayer containing carbon particles, fluorine resin, and water holdingmaterial arranged thereon.

Furthermore, the anode diffusion layer of the present invention isrequired to have water absorption ratio at 60° C. in a range of 40 to85% by arranging water holding layer containing 5 to 20 wt % of waterholding material which increases water holding property to the totalamount of electron conductive material and water holding material, onthe carbon-based material, or by containing carbon particles havingwater absorption amount at saturated water vapor pressure at 60° C. ofnot less than 150 cc/g. FIG. 1 is a graph showing a relationship ofcontent ratio of the water holding material to the total amount ofelectron conductive material and water holding material, and voltagedecrease. FIG. 2 is a graph showing a relationship of water absorptionamount of carbon particles and voltage decrease. As is clear from thesefigures, if the content ratio of the water holding material is in arange of 5 to 20 wt %, or if the water absorption amount of the carbonparticles is not less than 150 cc/g, voltage decrease is not more than30 mV, and desirable voltage efficiency is exhibited. FIG. 3 is a graphshowing a relationship of water absorption ratio of the anode diffusionlayer at 60° C. and voltage decrease. As is clear from FIG. 3, if thewater absorption ratio of the anode diffusion layer is in a range of 40to 85%, voltage decrease is not more than 30 mV, and desirable voltageefficiency is exhibited. On the other hand, if the content amount of thewater holding material or water absorption amount of the carbonparticles are below the range mentioned above, water absorption ratio ofthe anode diffusion layer is too low, and the above-mentioned effectcannot be obtained. If the content amount of the water holding materialor water absorption amount of the carbon particles are above the rangementioned above, water absorption ratio of the anode diffusion layer istoo high, gas supplying property is deteriorated by flooding phenomenon,and fuel shortage area is increased. As the water holding material ofthe present invention, oxides such as zeolite, γ-alumina, or silica canbe used.

In the present invention, differential pressure measured by adifferential pressure measuring method must be in a range of 60 to 120mmaq. FIG. 4 is a graph showing a relationship of differential pressureof the anode diffusion layer and voltage decrease. As is clear from FIG.4, if the differential pressure of the anode diffusion layer is in arange of 60 to 120 mmaq, voltage decrease is not more than 30 mV, anddesirable voltage efficiency is exhibited. On the other hand, if thedifferential pressure is above 120 mmaq, gas supplying property isdeteriorated, and fuel shortage area is increased. If the differentialpressure is below 60 mmaq, supplying protons only by electrolysis ofwater is not sufficient since the water exhausting property is high, andcorrosion reaction of carbon material in the anode is promoted. Thedifferential pressure measuring method mentioned herein is a method inwhich anode diffusion layer is set and held at mid-stream of a gas flowpassage, a pre-determined flow amount of reaction gas is flowed,pressures in front of and behind the anode diffusion layer are measured,and the difference in the pressures is calculated.

Furthermore, if adhesion of the polymer electrolyte membrane and theanode catalytic layer is not sufficient, protons generated byelectrolysis of water cannot be supplied to the polymer electrolytemembrane appropriately. Therefore, in the present invention, appropriatedegree of adhesion is expressed by a measured value of the cyclicvoltammetric method. That is, adhesion ratio in the present invention isdefined by the following formula.Adhesion ratio (%)=(Measured value by cyclic voltammetric method undercondition of one side humidified)/(Measured value by cyclic voltammetricmethod under condition of both side humidified)×100The cyclic voltammetric method under conditions of both sides humidifiedas mentioned herein is a method in which humidified gas is supplied toboth anode and cathode to humidify the entire electrode assembly and theamount of electric charge of all the catalytic material of all of theelectrode catalytic layer depending on electrochemical surface area ismeasured. On the other hand, the cyclic voltammetric method underconditions of one side humidified as mentioned herein is a method inwhich humidified gas is supplied only from the anode, the water suppliedfrom the anode is dispersed only to conductive passages of the polymermembrane of the cathode side, and the amount of electric charge of thecatalytic material of the cathode catalytic layer existing from thepolymer electrolyte membrane to proton conductive passages depending onelectrochemical surface area is measured. If the amount of the catalyticmaterial of the cathode catalytic layer existing from the polymerelectrolyte membrane to proton conductive passages becomes larger, theadhesion ratio becomes larger and the catalytic material is effectivelyused.

FIG. 5 is a graph showing a relationship of adhesion ratio and voltagedecrease. As is clear from FIG. 5, if the adhesion ratio is not lessthan 15%, voltage decrease is not more than 30 mV, and desirable voltageefficiency is exhibited. Therefore, in the present invention, it isnecessary that the ratio of quantity of electric charge of catalyticmaterial of the cathode catalytic layer existing in proton conductivepassage from the polymer electrolyte membrane measured by the cyclicvoltammetric method be not less than 15% of the quantity of electriccharge of all of the catalytic material existing in the cathodecatalytic layer.

In the electrode assembly of the present invention, it is desirable thata resistance overvoltage loss at 1 A/cm² be less than 10 mV. FIG. 6 is agraph showing the relationship of penetration resistance and voltageloss at 1 A/cm². As is clear from FIG. 6, if the penetration resistanceis not more than 5 mΩ, the voltage loss at 1 A/cm² is less than 10 mV,and desirable voltage efficiency is exhibited.

Furthermore, carbon-based material of the anode diffusion layer in thirdembodiment is limited to the carbon material which is processed to behydrophilic and not more than 90° of contact angle with water. It isnecessary to prepare water absorption ratio of the anode diffusion layerat 60° C. in a range of 40 to 85% by arranging a layer having fluorineresin and carbon particles whose water absorption amount at saturatedwater vapor pressure at 60° C. is not less than 150 cc/g, on thiscarbon-based material. FIG. 7 is a graph showing a relationship ofcontact angle of the carbon-based material with water and voltagedecrease. As is clear from FIGS. 7 and 2, if the contact angle ofcarbon-based material with water is not more than 90° and if the waterabsorption amount of the carbon particles is not less than 150 cc/g,voltage decrease is not more than 30 mV, desirable voltage efficiency isexhibited. FIG. 8 is a graph showing a relationship of water absorptionratio of the anode diffusion layer at 60° C. and the voltage decrease.Also in this embodiment, as is clear from FIG. 8, if the waterabsorption ratio of the anode diffusion layer is in a range of 40 to85%, voltage decrease is not more than 30 mV, desirable voltageefficiency is exhibited. However, if the contact angle of thecarbon-based material is above the range, water absorbed in the anodediffusion layer goes to the anode catalytic layer, flooding phenomenonoccurs in the anode catalytic layer, gas supplying property isdeteriorated, and area of fuel shortage under fuel shortage conditionsis enlarged. If the water absorption amount of the carbon particles isbelow the range, the effect of the present invention cannot be obtainedsince the water absorption ratio is too low. On the other hand, thewater absorption amount of the carbon particles is above the range, gassupplying property is deteriorated by the flooding phenomenon and areaof fuel shortage under fuel shortage conditions is enlarged since thewater absorption ratio of the anode diffusion layer is too high.

Also, in this embodiment, according to the same reason mentioned above,it is necessary that the differential pressure measured by thedifferential pressure measuring method be in a range from 60 to 120mmaq. FIG. 9 is a graph showing a relationship of the differentialpressure of the anode diffusion layer and the voltage decrease.

FIG. 10 is a graph showing a relationship of adhesion ratio and thevoltage decrease in this embodiment. As is clear from FIG. 10, if theadhesion ratio is not less than 15%, the voltage decrease is not morethan 30 mV, desirable voltage efficiency is exhibited. Therefore, in thepresent invention, it is necessary that the ratio of the quantity ofelectric charge of catalytic material of the cathode catalytic layerexisting in proton conductive passage from the polymer electrolytemembrane measured by a cyclic voltammetric method be not less than 15%to the quantity of electric charge of all the catalytic materialexisting in the cathode catalytic layer.

In an electrode assembly for the polymer electrolyte fuel cell of theforth embodiment of the present invention, void forming agent is addedto the cathode catalytic layer to prevent flooding in the cathodecatalytic layer, and water-repellant carbon particles are used in thecathode diffusion layer to supply water which is generated in thecathode or supplied from outside, to the anode side smoothly by reversediffusion. It is necessary that this water repellant carbon particlehave water absorption amount at saturated water vapor pressure at 60° C.of less than 150 cc/g. FIG. 11 is a graph showing a relationship ofwater absorption amount of the carbon particles in the cathode diffusionlayer of this embodiment and voltage decrease. As is clear from FIG. 11,if the water absorption amount of the carbon particles in the cathodediffusion layer is less than 150 cc/g, voltage decrease is not more than30 mV, desirable voltage efficiency is exhibited.

Since hydrophilic carbon particles are used in the anode diffusion layerof this embodiment, water can be retained. In the case in which fuel isin short supply, the retained water is supplied to the anode catalyticlayer to promote electrolysis of water, generated protons are suppliedto electrolyte membrane, and reverse diffusion water from the cathodeside can also be used in the electrolysis of water in the anodecatalytic layer. In this way, corrosion of carbon which is a next stepof the electrolysis of water is difficult to occur. It is necessary thatthe hydrophilic carbon particle have water absorption amount atsaturated water vapor pressure at 60° C. of not less than 150 cc/g. FIG.12 is a graph showing a relationship of water absorption amount ofcarbon particles in the anode diffusion layer of this embodiment andvoltage decrease. As is clear from FIG. 12, if the water absorptionamount of the carbon particles in the anode diffusion layer is not lessthan 150 cc/g, voltage decrease is not more than 30 mV, desirablevoltage efficiency is exhibited. Furthermore, it is necessary that theanode diffusion layer having high water holding property by adding thehydrophilic carbon particles have water absorption ratio at 60° C. in arange of 40 to 85%. FIG. 13 is a graph showing a relationship of waterabsorption ratio of the anode diffusion layer of this embodiment at 60°C. and voltage decrease. As is clear from FIG. 13, also in thisembodiment, if the water absorption ratio of the anode diffusion layeris in a range of 40 to 85%, voltage decrease is not more than 30 mV,desirable voltage efficiency is exhibited.

It is desirable that the carbon-based material of the cathode diffusionlayer of this embodiment be processed to be water-repellent and to havea contact angle with water of not less than 130°, and it is desirablethat the carbon-based material of the anode diffusion layer be processedto have a contact angle with water of not more than 90°. In this way,balance of water holding property of the cathode and anode can becontrolled, that is, not only can water be contained in the anodediffusion layer but also generated water in the cathode migrate to theanode to utilize the reverse diffusion water efficiently. In this way,electrolysis of water in the anode catalytic layer can be promoted moreefficiently, to improve restraining effect of carbon corrosion reaction.FIG. 14 is a graph showing a relationship of contact angle of thecarbon-based material with water in the cathode diffusion layer andvoltage decrease, and FIG. 15 is a graph showing a relationship ofcontact angle of the carbon-based material with water in the anodediffusion layer and voltage decrease. As is clear from these FIGS. 14and 15, if the contact angle of the carbon-based material of the cathodediffusion layer is not less than 130° or if the contact angle of thecarbon-based material of the anode diffusion layer is not more than 90°,voltage decrease is not more than 30 mV, and desirable voltageefficiency is exhibited. However, if the contact angle of thecarbon-based material of the cathode diffusion layer is less than 130°,flooding phenomenon occurs by the generated water in the cathode,reducing gas supplying property, and area of fuel shortage under fuelshortage conditions is enlarged. On the other hand, if the contact angleof the carbon-based material of the anode diffusion layer is more than90°, water absorbed in the anode diffusion layer is migrated to theanode catalytic layer, flooding phenomenon occurs in the anode catalyticlayer, reducing gas supplying property, and area of fuel shortage underfuel shortage conditions is enlarged.

Also in this embodiment, differential pressure of the cathode and anodemeasured by the differential pressure method must be in a range of 60 to120 mmaq. FIG. 16 is a graph showing a relationship of the differentialpressure of the cathode diffusion layer and voltage decrease, and FIG.17 is a graph showing a relationship of the differential pressure of theanode diffusion layer and voltage decrease. As is clear from FIGS. 16and 17, if the differential pressure of the cathode diffusion layer andthe anode diffusion layer is in a range of 60 to 120 mmaq, voltagedecrease is not more than 30 mV, and desirable voltage efficiency isexhibited. The differential pressures of the anode diffusion layer andthe cathode diffusion layer are closely associated with each other; forexample, even if the water absorption ratio of anode diffusion layer at60° C. is in an appropriate range, gas diffusion water amount cannot beefficiently controlled in the case in which the differential pressure ofthe cathode diffusion layer is not in an appropriate range.

Furthermore, if adhesion property of the polymer electrolyte membraneand the cathode catalytic layer is not sufficient, the above-mentionedreverse diffusion water cannot be supplied appropriately, and ifadhesion property of the polymer electrolyte membrane and the anodecatalytic layer is not sufficient, protons generated by electrolysis ofwater cannot be supplied to the polymer electrolyte membraneappropriately. Therefore, in the present invention, the degree ofappropriate adhesion property is expressed by a measured value by thecyclic voltammetric method.

FIG. 10 is a graph showing a relationship of adhesion ratio and voltagedecrease. As is clear from FIG. 10, if the adhesion ratio is not lessthan 15%, voltage decrease is not more than 30 mV, and desirable voltageefficiency is exhibited. Therefore, in the present invention, it isnecessary that the ratio of quantity of electric charge of catalyticmaterial of the cathode catalytic layer existing in proton conductivepassage from the polymer electrolyte membrane measured by a cyclicvoltammetric method be not less than 15% to the quantity of electriccharge of all the catalytic material existing in the cathode catalyticlayer.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph showing a relationship of content ratio of waterholding material to the total amount of electron conductive material andthe water holding material and voltage decrease in the first and secondembodiments.

FIG. 2 is a graph showing a relationship of water absorption amount ofcarbon particles and voltage decrease in the first, second, and thirdembodiments.

FIG. 3 is a graph showing a relationship of water absorption ratio ofanode diffusion layer at 60° C. and voltage decrease in the first andsecond embodiments.

FIG. 4 is a graph showing a relationship of differential pressure of theanode diffusion layer and voltage decrease in the first and secondembodiments.

FIG. 5 is a graph showing a relationship of adhesion ratio and voltagedecrease in the first and second embodiments.

FIG. 6 is a graph showing a relationship of penetration resistance andvoltage loss at 1 A/cm² in the first and second embodiments.

FIG. 7 is a graph showing a relationship of contact angle ofcarbon-based material with water and voltage decrease in the first andsecond embodiments.

FIG. 8 is a graph showing a relationship of water absorption ratio ofthe anode diffusion layer at 60° C. and voltage decrease in the thirdembodiment.

FIG. 9 is a graph showing a relationship of differential pressure of theanode diffusion layer and voltage decrease in the third embodiment.

FIG. 10 is a graph showing a relationship of adhesion ratio and voltagedecrease in the third and fourth embodiments.

FIG. 11 is a graph showing a relationship of water absorption amount ofcarbon particles in the cathode diffusion layer and voltage decrease inthe fourth embodiment.

FIG. 12 is a graph showing a relationship of water absorption amount ofcarbon particles in the anode diffusion layer and voltage decrease inthe fourth embodiment.

FIG. 13 is a graph showing a relationship of water absorption ratio inthe anode diffusion layer at 60° C. and voltage decrease in the fourthembodiment.

FIG. 14 is a graph showing a relationship of contact angle ofcarbon-based material with water in the cathode diffusion layer andvoltage decrease in the fourth embodiment.

FIG. 15 is a graph showing a relationship of contact angle ofcarbon-based material with water in the anode diffusion layer andvoltage decrease in the fourth embodiment.

FIG. 16 is a graph showing a relationship of differential pressure ofthe cathode diffusion layer and voltage decrease in the fourthembodiment.

FIG. 17 is a graph showing a relationship of differential pressure ofthe anode diffusion layer and voltage decrease in the fourth embodiment.

FIG. 18 is a graph showing a change of current density with time at afuel shortage test.

EXAMPLES

The electrode assembly for polymer electrolyte fuel cell of the presentinvention is further explained by way of Examples and ComparativeExamples.

A. FIRST EMBODIMENT

First, an embodiment in which a water holding layer is arranged on theanode diffusion layer, is explained. The water holding layer includescarbon-based material and 5 to 20 wt % of water holding material to thetotal amount of electron conductive material and the water holdingmaterial.

1. Preparation of Electrode Assembly

Example 1

35 g of ion conductive polymer (trade name: Nafion SE20192, produced byDu Pont), 10 g of platinum supporting carbon particles in which theweight ratio of carbon black to platinum is 50:50 (trade name:TEC10E50E, produced by Tanaka Kikinzoku Kogyo K. K.), and 2.5 g ofcrystalline carbon fiber (trade name: VGCF, produced by Showa Denko)were mixed to prepare cathode catalytic paste. This cathode catalyticpaste was coated on a FEP sheet so that the Pt amount is 0.3 mg/cm², andwas dried to prepare a cathode electrode sheet. On the other hand, 36.8g of ion conductive polymer (trade name: Nafion SE20192, produced by DuPont) and 10 g of Pt—Ru supporting carbon particles in which weightratio of the carbon black and the catalyst is 46:54 (trade name:TEC61E54, Pt:Ru=1:1, Tanaka Kikinzoku Kogyo K. K.) were mixed to preparean anode catalytic paste. This anode catalytic paste was coated to a FEPsheet so that catalyst amount is 0.15 mg/cm², and dried to prepare ananode electrode sheet.

25 g of ion conductive polymer (trade name: Nafion SE20192, produced byDu Pont), 4.5 g of carbon black (trade name: Vulcan XC75, produced byCabot), 2.5 g of crystalline carbon fiber (trade name: VGCF, produced byShowa Denko), and 0.5 g of ZSM5 (produced by Tosoh Corporation) weremixed to prepare a foundation paste A1. 12 g of Teflon (trademark)powder (trade name: L170J, produced by Asahi Glass Co., Ltd.) and 18 gof carbon black powder (trade name: Vulcan XC75, produced by Cabot) weremixed with ethylene glycol to prepare a foundation paste B1. Next, thefoundation paste B1 was coated on a carbon paper (trade name: TGP060,produced by Toray Industries Inc.) which was beforehand process to bewater-repellant so as to be 2.3 mg/cm², the foundation paste A1 wascoated so as to be 0.3 mg/cm², and dried, to prepare an anode diffusionlayer. On the other hand, only the foundation paste B1 was coated on thesame carbon paper so as to be 2.3 mg/cm², and was dried to obtain acathode diffusion layer.

The electrode sheets of the anode and cathode are transferred to anelectrolyte membrane by a decal method (unifying pressure of 40 kg/cm²)to prepare membrane electrode assembly CCM. The anode diffusion layerand the cathode diffusion layer mentioned above, were layered on bothsides of the CCM to form electrode assembly MEA of Example 1.

Example 2

Except that a foundation paste A2 was used instead of the foundationpaste A1, a membrane electrode assembly MEA of Example 2 was prepared ina manner similar to that of Example 1. It should be noted that thefoundation paste A2 was prepared by mixing 25 g of ion conductivepolymer (trade name: Nafion SE20192, produced by Du Pont), 4.0 g ofcarbon black powder (trade name: Vulcan XC75, produced by Cabot), 2.5 gof crystalline carbon fiber (trade name: VGCF, produced by Showa Denko),and 1 g of ZSM5 (produced by Tosoh Corporation).

Example 3

Except that a foundation paste A3 was used instead of the foundationpaste A1, a membrane electrode assembly MEA of Example 3 was prepared ina manner similar to that of Example 1. It should be noted that thefoundation paste A3 was prepared by mixing 25 g of ion conductivepolymer (trade name: Nafion SE20192, produced by Du Pont), 4.75 g ofcarbon black powder (trade name: Vulcan XC75, produced by Cabot), 2.5 gof crystalline carbon fiber (trade name: VGCF, produced by Showa Denko),and 0.25 g of ZSM5 (produced by Tosoh Corporation).

Example 4

Except that a foundation paste A4 was used instead of the foundationpaste A1, a membrane electrode assembly MEA of Example 4 was prepared ina manner similar to that of Example 1. It should be noted that thefoundation paste A4 was prepared by mixing 25 g of ion conductivepolymer (trade name: Nafion SE20192, produced by Du Pont), 4.5 g ofcarbon black powder (trade name: Vulcan XC75, produced by Cabot), and0.5 g of ZSM5 (produced by Tosoh Corporation).

Example 5

Except that an anode diffusion layer in which a foundation paste B2 wascoated on a carbon paper (trade name: TP060, produced by TorayIndustries Inc.) beforehand treated to be water-repellent and dried soas to be 2.3 mg/cm², was used instead of the anode diffusion layer ofExample 1, a membrane electrode assembly MEA of Example 5 was preparedin a manner similar to that of Example 1. It should be noted that thefoundation paste B2 was prepared by mixing 12 g of Teflon (trademark)powder (trade name: L170J, produced by Asahi Glass Co., Ltd.), 16.2 g ofcarbon black powder (trade name: Vulcan XC75, produced by Cabot), and1.8 g of ZSM5 (produced by Tosoh Corporation) with ethylene glycol.

Comparative Example 1

Except that a foundation paste A5 was used instead of the foundationpaste A1, a membrane electrode assembly MEA of Comparative Example 1 wasprepared in a manner similar to that of Example 1. It should be notedthat the foundation paste A5 was prepared by mixing 25 g of ionconductive polymer (trade name: Nafion SE20192, produced by Du Pont),3.75 g of carbon black powder (trade name: Vulcan XC75, produced byCabot), 2.5 g of crystalline carbon fiber (trade name: VGCF, produced byShowa Denko), and 1.25 g of ZSM5 (produced by Tosoh Corporation).

Comparative Example 2

Except that a foundation paste A6 was used instead of the foundationpaste A1, a membrane electrode assembly MEA of Comparative Example 2 wasprepared in a manner similar to that of Example 1. It should be notedthat the foundation paste A6 was prepared by mixing 30 g of ionconductive polymer (trade name: Nafion SE20192, produced by Du Pont),4.5 g of carbon black powder (trade name: Vulcan XC75, produced byCabot), and 0.5 g of ZSM5 (produced by Tosoh Corporation).

Comparative Example 3

Except that a foundation paste A7 was used instead of the foundationpaste A1, a membrane electrode assembly MEA of Comparative Example 3 wasprepared in a manner similar to that of Example 1. It should be notedthat the foundation paste A7 was prepared by mixing 35 g of ionconductive polymer (trade name: Nafion SE20192, produced by Du Pont),4.5 g of carbon black powder (trade name: Vulcan XC75, produced byCabot), and 0.5 g of ZSM5 (produced by Tosoh Corporation).

Comparative Example 4

Except that a foundation paste A8 was used instead of the foundationpaste A1, a membrane electrode assembly MEA of Comparative Example 4 wasprepared in a manner similar to that of Example 1. It should be notedthat the foundation paste A8 was prepared by mixing 25 g of ionconductive polymer (trade name: Nafion SE20192, produced by Du Pont), 5g of carbon black powder (trade name: Vulcan XC75, produced by Cabot),and 2.5 g of crystalline carbon fiber (trade name: VGCF, produced byShowa Denko).

Comparative Example 5

Except that a foundation paste A9 was used instead of the foundationpaste A1, a membrane electrode assembly MEA of Comparative Example 5 wasprepared in a manner similar to that of Example 1. It should be notedthat the foundation paste A9 was prepared by mixing 25 g of ionconductive polymer (trade name: Nafion SE20192, produced by Du Pont),4.5 g of carbon black powder (trade name: Vulcan XC75, produced byCabot), 1.5 g of crystalline carbon fiber (trade name: VGCF, produced byShowa Denko), and 0.5 g of ZSM5 (produced by Tosoh Corporation).

Comparative Example 6

Except that a foundation paste A10 was used instead of the foundationpaste A1, a membrane electrode assembly MEA of Comparative Example 6 wasprepared in a manner similar to that of Example 1. It should be notedthat the foundation paste A10 was prepared by mixing 25 g of ionconductive polymer (trade name: Nafion SE20192, produced by Du Pont),4.5 g of carbon black powder (trade name: Vulcan XC75, produced byCabot), 3.5 g of crystalline carbon fiber (trade name: VGCF, produced byShowa Denko), and 0.5 g of ZSM5 (produced by Tosoh Corporation).

Comparative Example 7

Except that the unifying pressure of the decal method in the productionof the membrane electrode assembly CCM was 30 kg/cm², a membraneelectrode assembly MEA of Comparative Example 7 was prepared in a mannersimilar to that of Example 1.

Comparative Example 8

Except that the unifying pressure of the decal method in the productionof the membrane electrode assembly CCM was 10 kg/cm², a membraneelectrode assembly of Comparative Example 8 was prepared in a mannersimilar to that of Example 1.

2. Fuel Shortage Test

A fuel shortage test was performed on fuel cells containing membraneelectrode assemblies of Examples and Comparative Examples mentionedabove. The test conditions were as follows: cell temperature: 80° C.,humidity amount: 45 RH % in the anode and 85 RH % in the cathode,utilization ratio at 0.5 A/cm²: 100% in the anode and 60% in thecathode. Current density of the test was changed from 0 to 1 A/cm² overtime as shown in FIG. 18, and this change was repeated 500 times. Adifference of voltage calculated by terminal voltages before and afterthe fuel test is shown in Table 1. TABLE 1 Content ratio Waterabsorption of water ratio of Differential Adhesion Penetration holdinganode diffusion pressure ratio resistance Δ voltage material (wt %)layer (wt %) (mmaq) (%) (mΩ) (mV) Example 1 10 65 90 20 3.2 12 Example 220 75 115 22 3.8 27.6 Example 3 5 46 62 18 2.8 25 Example 4 10 62 75 194.4 21 Example 5 10 62 78 21 4.8 22 Comparative Example 1 25 83 82 234.4 52 Comparative Example 2 10 90.8 70 21 4.6 36 Comparative Example 310 93.9 63 20 4.8 43 Comparative Example 4 0 35 30 18 2.6 65 ComparativeExample 5 10 72 50 16 3.8 62 Comparative Example 6 10 76 125 18 4.2 37.3Comparative Example 7 10 65 93 12 3.4 42 Comparative Example 8 10 65 888 4.6 583. Evaluation

The electrode assemblies of Examples 1 to 5 in which content ratio ofthe water holding material, water absorption ratio of the anodediffusion layer, differential pressure, and adhesion ratio are withinthe range of the present invention, have penetration resistance of notmore than 5 mΩ and difference of voltage at the fuel shortage test ofnot more than 30 mV. Efficiencies were not reduced very much. On theother hand, the electrode assembly of Comparative Example 1 having toohigh content ratio of water holding material, the electrode assembliesof Comparative Examples 2 and 3 having too high water absorption ratioof the anode diffusion layer, the electrode assembly of ComparativeExample 4 having too low content ratio of water holding material, waterabsorption ratio of the anode diffusion layer and differential pressure,the electrode assembly of Comparative Example 5 having too lowdifferential pressure, the electrode assembly of Comparative Example 6having too high differential pressure, and the electrode assemblies ofComparative Examples 7 and 8 having too low adhesion ratio, all havepenetration resistance of not more than 5 mΩ; however, difference ofvoltage in the fuel shortage test exceeds more than 30 mV. Efficiencieswere reduced very much.

B. SECOND EMBODIMENT

Next, an embodiment in which carbon particles having water absorptionamount at saturated water vapor pressure at 60° C. of not less than 150cc/g are contained in the anode diffusion layer, is explained.

1. Preparation of Electrode Assembly

Example 6

Except that a foundation paste A11 was used instead of the foundationpaste A1, a membrane electrode assembly MEA of Example 6 was prepared ina manner similar to that of Example 1. It should be noted that thefoundation paste A11 was prepared by mixing 25 g of ion conductivepolymer (trade name: Nafion SE20192, produced by Du Pont), 5 g of carbonblack powder (trade name: Ketjen black, produced by Cabot), and 2.5 g ofcrystalline carbon fiber (trade name: VGCF, produced by Showa Denko).

Example 7

Except that a foundation paste A12 was used instead of the foundationpaste A1, a membrane electrode assembly MEA of Example 7 was prepared ina manner similar to that of Example 1. It should be noted that thefoundation paste A12 was prepared by mixing 25 g of ion conductivepolymer (trade name: Nafion SE20192, produced by Du Pont), and 5 g ofcarbon black powder (trade name: Ketjen black, produced by Cabot).

Example 8

Except that an anode diffusion layer in which a foundation paste A13 wascoated on a carbon paper (trade name: TP060, produced by TorayIndustries Inc.) treated beforehand to be water-repellent and dried soas to be 2.3 mg/cm², is used instead of the anode diffusion layer ofExample 1, a membrane electrode assembly MEA of Example 8 was preparedin a manner similar to that of Example 1. It should be noted that thefoundation paste A13 was prepared by mixing 12 g of Teflon (trademark)dispersion (trade name: L170J, produced by Asahi Glass Co., Ltd.), and18 g of carbon black powder (trade name: Ketjen black, produced byCabot).

Comparative Example 9

Except that a foundation paste A14 was used instead of the foundationpaste A1, a membrane electrode assembly MEA of Comparative Example 9 wasprepared in a manner similar to that of Example 1. It should be notedthat the foundation paste A14 was prepared by mixing 25 g of ionconductive polymer (trade name: Nafion SE20192, produced by Du Pont), 5g of carbon black powder (trade name: AB-5, produced by Cabot), and 2.5g of crystalline carbon fiber (trade name: VGCF, produced by ShowaDenko).

Comparative Example 10

Except that a foundation paste A15 was used instead of the foundationpaste A1, a membrane electrode assembly MEA of Comparative Example 10was prepared in a manner similar to that of Example 1. It should benoted that the foundation paste A15 was prepared by mixing 25 g of ionconductive polymer (trade name: Nafion SE20192, produced by Du Pont), 5g of carbon black powder (trade name: Vulcan XC75, produced by Denka),and 2.5 g of crystalline carbon fiber (trade name: VGCF, produced byShowa Denko).

Comparative Example 11

Except that a foundation paste A16 was used instead of the foundationpaste A1, a membrane electrode assembly MEA of Comparative Example 11was prepared in a manner similar to that of Example 1. It should benoted that the foundation paste A16 was prepared by mixing 18 g of ionconductive polymer (trade name: Nafion SE20192, produced by Du Pont), 5g of carbon black powder (trade name: Ketjen black, produced by Cabot),and 3.5 g of crystalline carbon fiber (trade name: VGCF, produced byShowa Denko).

Comparative Example 12

Except that a foundation paste A17 was used instead of the foundationpaste A1, a membrane electrode assembly MEA of Comparative Example 12was prepared in a manner similar to that of Example 1. It should benoted that the foundation paste A17 was prepared by mixing 25 g of ionconductive polymer (trade name: Nafion SE20192, produced by Du Pont), 5g of carbon black powder (trade name: Ketjen black, produced by Cabot),and 3.5 g of crystalline carbon fiber (trade name: VGCF, produced byShowa Denko).

Comparative Example 13

Except that a foundation paste A18 was used instead of the foundationpaste A1, a membrane electrode assembly MEA of Comparative Example 13was prepared in a manner similar to that of Example 1. It should benoted that the foundation paste A18 was prepared by mixing 30 g of ionconductive polymer (trade name: Nafion SE20192, produced by Du Pont), 5g of carbon black powder (trade name: Ketjen black, produced by Cabot),and 1 g of crystalline carbon fiber (trade name: VGCF, produced by ShowaDenko).

Comparative Example 14

Except that the unifying pressure of the decal method in the productionof the membrane electrode assembly CCM was 30 kg/cm², a membraneelectrode assembly MEA of Comparative Example 14 was prepared in amanner similar to that of Example 6.

Comparative Example 15

Except that the unifying pressure of the decal method in the productionof the membrane electrode assembly CCM was 10 kg/cm², a membraneelectrode assembly MEA of Comparative Example 15 was prepared in amanner similar to that of Example 6.

2. Fuel Shortage Test

A fuel shortage test was performed about fuel cells containing membraneelectrode assemblies of Examples and Comparative Examples mentionedabove. The test conditions were the same as the test of the firstembodiment described above. A difference of voltage calculated byterminal voltages before and after the fuel test is shown in Table 2.TABLE 2 Water absorption amount of Water absorption carbon ratio ofDifferential Adhesion Penetration particles anode diffusion pressureratio resistance Δ voltage (cc/g) layer (wt %) (mmaq) (%) (mΩ) (mV)Example 6 360 52 62 20 3.2 26 Example 7 360 82 115 29 4.4 27.5 Example 8360 65 78 21 4.8 24 Example 9 130 40 82 23 4.4 32 Comparative Example 1080 21 70 19 4.2 65 Comparative Example 11 360 120 65 22 3.2 55Comparative Example 12 360 78 43.8 21 3.1 62 Comparative Example 13 36055 140 20 4.8 48 Comparative Example 14 360 65 93 12 3.4 35.8Comparative Example 15 360 65 88 8 4.6 583. Evaluation

The electrode assemblies of Examples 6 to 8 in which water absorptionamount of carbon particles, water absorption ratio of the anodediffusion layer, differential pressure, and adhesion ratio are withinthe range of the present invention, have penetration resistance of notmore than 5 mΩ and difference of voltage at the fuel shortage test ofnot more than 30 mV. Efficiencies were not deteriorated so much. On theother hand, the electrode assembly of Comparative Example 9 having toohigh water absorption amount of carbon particles, the electrode assemblyof Comparative Example 10 having too low water absorption amount ofcarbon particles and too low water absorption ratio of anode diffusionlayer, the electrode assemblies of Comparative Example 11 having toohigh water absorption ratio of the anode diffusion layer, the electrodeassembly of Comparative Example 12 having too low differential pressure,the electrode assembly of Comparative Example 13 having too highdifferential pressure, and the electrode assemblies of ComparativeExamples 14 and 15 having too low adhesion ratio, all have penetrationresistance of not more than 5 mΩ; however, difference of voltage at thefuel shortage test exceeds more than 30 mV. Efficiencies were decreasedvery much.

C. THIRD EMBODIMENT

1. Preparation of Electrode Assembly

Example 9

35 g of ion conductive polymer (trade name: Nafion SE20192, produced byDu Pont), 10 g of platinum supporting carbon particles in which weightratio of carbon black and platinum is 50:50 (trade name: TEC10E50E,produced by Tanaka Kikinzoku Kogyo K. K.), and 2.5 g of crystallinecarbon fiber (trade name: VGCF, produced by Showa Denko) were mixed toprepare cathode catalytic paste. This cathode catalytic paste was coatedto a FEP sheet so that Pt amount is 0.3 mg/cm², and dried to prepare acathode electrode sheet. On the other hand, 36.8 g of ion conductivepolymer (trade name: Nafion SE20192, produced by Du Pont) and 10 g ofPt—Ru supporting carbon particles in which weight ratio of the carbonblack and the catalyst is 46:54 (trade name: TEC61E54, Pt:Ru=1:1, TanakaKikinzoku Kogyo K. K.) were mixed to prepare an anode catalytic paste.This anode catalytic paste was coated to a FEP sheet so that catalystamount is 0.15 mg/cm², and dried to prepare an anode electrode sheet.

On the other hand, a carbon paper (trade name: TGP060, produced by TorayIndustries Inc.) was immersed into water at 95° C. in a pressureresistant container for 100 hours to perform hydrophilic treatment sothat contact angle with water is 75°.

25 g of ion conductive polymer (trade name: Nafion SE20192, produced byDu Pont) and 5 g of carbon black powder (trade name: Ketjen black,produced by Cabot) were mixed to prepare a foundation paste C1. 12 g ofTeflon (trademark) powder (trade name: L170J, produced by Asahi GlassCo., Ltd.) and 18 g of carbon black powder (trade name: Vulcan XC75,produced by Cabot) were mixed with ethylene glycol to prepare afoundation paste D1. Next, the foundation paste C1 was coated on thecarbon paper treated to be hydrophilic as described above so as to be1.0 mg/cm², and dried to prepare an anode diffusion layer. On the otherhand, the foundation paste D1 was coated on the same carbon paper so asto be 2.3 mg/cm², and dried to obtain a cathode diffusion layer.

The electrode sheets of the anode and cathode are transferred to anelectrolyte membrane by a decal method (unifying pressure of 40 kg/cm²)to prepare membrane electrode assembly CCM. The anode diffusion layerand the cathode diffusion layer mentioned above, were layered on bothsides of the CCM to form electrode assembly MEA of Example 9.

Example 10

Except that coated amount of the foundation paste C1 of Example 9 was0.6 mg/cm², membrane electrode assembly MEA of Example 10 was preparedin a manner similar to that of Example 9.

Example 11

Except that a foundation paste C2 was used instead of the foundationpaste C1, a membrane electrode assembly MEA of Example 11 was preparedin a manner similar to that of Example 9. It should be noted that thefoundation paste C2 was prepared by mixing 12 g of Teflon (trademark)powder (trade name: L170J, produced by Asahi Glass Co., Ltd.) and 18 gof carbon black powder (trade name: Ketjen black, produced by Cabot)with ethylene glycol.

Example 12

Except that a foundation paste C3 was used instead of the foundationpaste C1, a membrane electrode assembly MEA of Example 12 was preparedin a manner similar to that of Example 9. It should be noted that thefoundation paste C3 was prepared by mixing 18 g of Teflon (trademark)powder (trade name: L170J, produced by Asahi Glass Co., Ltd.) and 12 gof carbon black powder (trade name: Ketjen black, produced by Cabot)with ethylene glycol.

Comparative Example 16

Except that the contact angle with water was set to 100° in thehydrophilic treatment of the carbon paper by controlling time ofimmersion into hot water, a membrane electrode assembly MEA ofComparative Example 16 was prepared in a manner similar to that ofExample 9.

Comparative Example 17

Except that the contact angle with water was set to 120° in thehydrophilic treatment of the carbon paper by controlling time ofimmersion into hot water, a membrane electrode assembly MEA ofComparative Example 17 was prepared in a manner similar to that ofExample 9.

Comparative Example 18

Except that the contact angle with water was set to 140° in thehydrophilic treatment of the carbon paper by controlling time ofimmersion into hot water, a membrane electrode assembly MEA ofComparative Example 18 was prepared in a manner similar to that ofExample 9.

Comparative Example 19

Except that a foundation paste C4 was used instead of the foundationpaste C1 and the coated amount was 1.8 mg/cm² in the anode diffusionlayer forming process, a membrane electrode assembly MEA of ComparativeExample 19 was prepared in a manner similar to that of Example 9. Itshould be noted that the foundation paste C4 was prepared by mixing 25 gof ion conductive polymer (trade name: Nafion SE20192, produced by DuPont) and 5 g of carbon black powder (trade name: AB-5, produced byCabot).

Comparative Example 20

Except that a foundation paste C5 was used instead of the foundationpaste C1 and the coated amount was 2.3 mg/cm² in the anode diffusionlayer forming process, a membrane electrode assembly MEA of ComparativeExample 20 was prepared in a manner similar to that of Example 9. Itshould be noted that the foundation paste C5 was prepared by mixing 25 gof ion conductive polymer (trade name: Nafion SE20192, produced by DuPont) and 5 g of carbon black powder (trade name: Vulcan XC75, producedby Cabot).

Comparative Example 21

Except that a foundation paste C6 was used instead of the foundationpaste C1 and the coated amount was 1.8 mg/cm² in the anode diffusionlayer forming process, a membrane electrode assembly MEA of ComparativeExample 21 was prepared in a manner similar to that of Example 9. Itshould be noted that the foundation paste C6 was prepared by mixing 40 gof ion conductive polymer (trade name: Nafion SE20192, produced by DuPont) and 5 g of carbon black powder (trade name: Ketjen black, producedby Cabot).

Comparative Example 22

Except that a foundation paste C7 was used instead of the foundationpaste C1 and the coated amount was 0.8 mg/cm² in the anode diffusionlayer forming process, a membrane electrode assembly MEA of ComparativeExample 22 was prepared in a manner similar to that of Example 9. Itshould be noted that the foundation paste C7 was prepared by mixing 15 gof ion conductive polymer (trade name: Nafion SE20192, produced byDuPont) and 5 g of carbon black powder (trade name: Ketjen black,produced by Cabot).

Comparative Example 23

Except that a foundation paste C8 was used instead of the foundationpaste C1 and the coated amount was 1.2 mg/cm² in the anode diffusionlayer forming process, a membrane electrode assembly MEA of ComparativeExample 23 was prepared in a manner similar to that of Example 9. Itshould be noted that the foundation paste C8 was prepared by mixing 35 gof ion conductive polymer (trade name: Nafion SE20192, produced by DuPont) and 5 g of carbon black powder (trade name: Ketjen black, producedby Cabot).

Comparative Example 24

Except that a foundation paste C9 was used instead of the foundationpaste C1, a membrane electrode assembly MEA of Comparative Example 24was prepared in a manner similar to that of Example 9. It should benoted that the foundation paste C9 was prepared by mixing 20 g of ionconductive polymer (trade name: Nafion SE20192, produced by Du Pont) and5 g of carbon black powder (trade name: Ketjen black, produced byCabot).

Comparative Example 25

Except that the unifying pressure of the decal method in the productionof the membrane electrode assembly CCM was 30 kg/cm², a membraneelectrode assembly MEA of Comparative Example 25 was prepared in amanner similar to that of Example 9.

Comparative Example 26

Except that the unifying pressure of the decal method in the productionof the membrane electrode assembly CCM was 10 kg/cm², a membraneelectrode assembly MEA of Comparative Example 26 was prepared in amanner similar to that of Example 9.

2. Fuel Shortage Test

Fuel shortage tests were performed on fuel cells containing membraneelectrode assemblies of Examples and Comparative Examples mentionedabove. The test conditions were the same as the test of the firstembodiment described above. Differences in voltage calculated byterminal voltages before and after the fuel test are shown in Table 3.TABLE 3 Contact Water Water angle of absorption absorption carbon-basedamount of ratio of anode Differential Adhesion Penetration materialcarbon particles diffusion layer pressure ratio resistance Δ voltage (°)(cc/g) (wt %) (mmaq) (%) (mΩ) (mV) Example 9 75 360 78.5 106 20 4.2 26Example 10 75 360 51.3 65.5 19 4.4 24 Example 11 75 360 65 78 21 4.8 24Example 12 75 360 55 87 20 4.4 26 Comparative Example 16 100 360 85 8223 4.4 32 Comparative Example 17 120 360 85 70 19 4.8 55 ComparativeExample 18 140 360 85 65 22 4.6 65 Comparative Example 19 75 130 62 7021 4.6 32 Comparative Example 20 75 80 47 62 20 4.8 65 ComparativeExample 21 75 360 98 103 18 4.4 36 Comparative Example 22 75 360 35 6221 4.2 42 Comparative Example 23 75 360 82 130 19 4.0 32 ComparativeExample 24 75 360 78 45 20 3.8 48 Comparative Example 25 75 360 65 93 124.5 35.8 Comparative Example 26 75 360 65 88 8 4.6 583. Evaluation

The electrode assemblies of Examples 9 to 12 in which contact angle ofcarbon-based material, water absorption amount of carbon particles,water absorption ratio of the anode diffusion layer, differentialpressure, and adhesion ratio are within the range of the presentinvention, have penetration resistance of not more than 5 mΩ anddifference of voltage at the fuel shortage test of not more than 30 mV.Efficiencies were not decreased very much. On the other hand, theelectrode assemblies of Comparative Examples 16 to 18 having too highcontact angle, the electrode assemblies of Comparative Examples 19 and20 having too low water absorption amount of carbon particles, theelectrode assembly of Comparative Example 21 having too high waterabsorption ratio of anode diffusion layer, the electrode assembly ofComparative Example 22 having too low water absorption ratio of anodediffusion layer, the electrode assembly of Comparative Example 23 havingtoo high differential pressure, the electrode assembly of ComparativeExample 24 having too low differential pressure, and the electrodeassemblies of Comparative Examples 25 and 26 having too low adhesionratio have penetration resistance of not more than 5 mΩ; however,difference of voltages in the fuel shortage test exceed 30 mV.Efficiencies were decreased very much.

D. FOURTH EMBODIMENT

1. Preparation of Electrode Assembly

Example 13

35 g of ion conductive polymer (trade name: Nafion SE20192, produced byDu Pont), 10 g of platinum supporting carbon particles in which weightratio of carbon black and platinum is 50:50 (trade name: TEC10E50E,produced by Tanaka Kikinzoku Kogyo K. K.), and 2.5 g of crystallinecarbon fiber (trade name: VGCF, produced by Showa Denko) were mixed toprepare a cathode catalytic paste. This cathode catalytic paste wascoated on a FEP sheet so that Pt amount is 0.3 mg/cm², and dried toprepare a cathode electrode sheet. On the other hand, 36.8 g of ionconductive polymer (trade name: Nafion SE20192, produced by Du Pont) and10 g of Pt—Ru supporting carbon particles in which weight ratio of thecarbon black and the catalyst is 46:54 (trade name: TEC61E54, Pt:Ru=1:1,Tanaka Kikinzoku Kogyo K. K.) were mixed to prepare an anode catalyticpaste. This anode catalytic paste was coated to a FEP sheet so thatcatalyst amount is 0.15 mg/cm², and dried to prepare an anode electrodesheet.

On the other hand, two sheets of carbon paper (trade name: TGP060,produced by Toray Industries Inc.) were immersed in water at 95° C. in apressure resistant container to perform hydrophilic treatment so thatcontact angle with water thereof become 140° and 75°, to prepare twosheets of carbon paper for a cathode diffusion layer and an anodediffusion layer mutually.

On the other hand, 12 g of Teflon (trademark) powder (trade name: L170J,produced by Asahi Glass Co., Ltd.) and 18 g of carbon black powder(trade name: Ketjen black, produced by Cabot) were mixed with ethyleneglycol to prepare a foundation paste E1, and 12 g of Teflon (trademark)powder (trade name: L170J, produced by Asahi Glass Co., Ltd.) and 18 gof carbon black powder (trade name: AB-5, produced by Cabot) were mixedwith ethylene glycol to prepare a foundation paste F1. Next, thefoundation paste E1 was coated to the carbon paper for anode diffusionlayer treated to be hydrophilic as described above so as to be 2.3mg/cm², and dried to obtain the anode diffusion layer. On the otherhand, the foundation paste F1 was coated on the carbon paper for cathodediffusion layer so as to be 2.3 mg/cm², and dried to obtain the cathodediffusion layer.

The electrode sheets of the anode and cathode are transferred to anelectrolyte membrane by a decal method (unifying pressure of 40 kg/cm²)to prepare membrane electrode assembly CCM. The anode diffusion layerand the cathode diffusion layer mentioned above, were layered on bothsides of the CCM to form electrode assembly MEA of Example 13.

Example 14

Except that a foundation paste F2 was used instead of the foundationpaste F1, a membrane electrode assembly MEA of Example 14 was preparedin a manner similar to that of Example 13. It should be noted that thefoundation paste F2 was prepared by mixing 12 g of Teflon (trademark)powder (trade name: L170J, produced by Asahi Glass Co., Ltd.) and 18 gof carbon black powder (trade name: VulcanXC75, produced by Cabot) withethylene glycol.

Example 15

Except that foundation pastes E2 and F3 were used instead of thefoundation pastes E1 and F1, a membrane electrode assembly MEA ofExample 15 was prepared in a manner similar to that of Example 13. Itshould be noted that the foundation paste E2 was prepared by mixing 9 gof Teflon (trademark) powder (trade name: L170J, produced by Asahi GlassCo., Ltd.) and 21 g of carbon black powder (trade name: Ketjen black,produced by Cabot) with ethylene glycol, and the foundation paste F3 wasprepared by mixing 9 g of Teflon (trademark) powder (trade name: L170J,produced by Asahi Glass Co., Ltd.) and 21 g of carbon black powder(trade name: AB-5, produced by Cabot) with ethylene glycol.

Example 16

Except that foundation pastes E3 and F4 were used instead of thefoundation pastes E1 and F1, a membrane electrode assembly MEA ofExample 16 was prepared in a manner similar to that of Example 13. Itshould be noted that the foundation paste E3 was prepared by mixing 21 gof Teflon (trademark) powder (trade name: L170J, produced by Asahi GlassCo., Ltd.) and 9 g of carbon black powder (trade name: Ketjen black,produced by Cabot) with ethylene glycol, and the foundation paste F4 wasprepared by mixing 21 g of Teflon (trademark) powder (trade name: L170J,produced by Asahi Glass Co., Ltd.) and 9 g of carbon black powder (tradename: AB-5, produced by Cabot) with ethylene glycol.

Comparative Example 27

Except that foundation paste F5 was used instead of the foundation pasteF1, a membrane electrode assembly MEA of Comparative Example 27 wasprepared in a manner similar to that of Example 13. It should be notedthat the foundation paste F5 was prepared by mixing 12 g of Teflon(trademark) powder (trade name: L170J, produced by Asahi Glass Co.,Ltd.) and 18 g of carbon black powder (trade name: Ketjen black,produced by Cabot) with ethylene glycol.

Comparative Example 28

Except that foundation paste F6 was used instead of the foundation pasteF1, a membrane electrode assembly MEA of Comparative Example 28 wasprepared in a manner similar to that of Example 13. It should be notedthat the foundation paste F6 was prepared by mixing 12 g of Teflon(trademark) powder (trade name: L170J, produced by Asahi Glass Co.,Ltd.) and 18 g of carbon black powder (trade name: Ketjen black 600JD,produced by Cabot) with ethylene glycol.

Comparative Example 29

Except that foundation paste E4 was used instead of the foundation pasteE1, a membrane electrode assembly MEA of Comparative Example 29 wasprepared in a manner similar to that of Example 13. It should be notedthat the foundation paste E4 was prepared by mixing 12 g of Teflon(trademark) powder (trade name: L170J, produced by Asahi Glass Co.,Ltd.) and 18 g of carbon black powder (trade name: AB-5, produced byCabot) with ethylene glycol.

Comparative Example 30

Except that foundation paste E5 was used instead of the foundation pasteE1, a membrane electrode assembly MEA of Comparative Example 30 wasprepared in a manner similar to that of Example 13. It should be notedthat the foundation paste E5 was prepared by mixing 12 g of Teflon(trademark) powder (trade name: L170J, produced by Asahi Glass Co.,Ltd.) and 18 g of carbon black powder (trade name: Vulcan XC75, producedby Cabot) with ethylene glycol.

Comparative Example 31

Except that foundation paste E6 was used instead of the foundation pasteE1, a membrane electrode assembly MEA of Comparative Example 31 wasprepared in a manner similar to that of Example 13. It should be notedthat the foundation paste E6 was prepared by mixing 24 g of Teflon(trademark) powder (trade name: L170J, produced by Asahi Glass Co.,Ltd.) and 6 g of carbon black powder (trade name: Ketjen black, producedby Cabot) with ethylene glycol.

Comparative Example 32

Except that foundation paste E7 was used instead of the foundation pasteE1, a membrane electrode assembly MEA of Comparative Example 32 wasprepared in a manner similar to that of Example 13. It should be notedthat the foundation paste E7 was prepared by mixing 6 g of Teflon(trademark) powder (trade name: L170J, produced by Asahi Glass Co.,Ltd.) and 24 g of carbon black powder (trade name: Ketjen black,produced by Cabot) with ethylene glycol.

Comparative Example 33

Except that foundation paste F7 was used instead of the foundation pasteE1, a membrane electrode assembly MEA of Comparative Example 33 wasprepared in a manner similar to that of Example 13. It should be notedthat the foundation paste F7 was prepared by mixing 24 g of Teflon(trademark) powder (trade name: L170J, produced by Asahi Glass Co.,Ltd.) and 6 g of carbon black powder (trade name: AB-5, produced byCabot) with ethylene glycol.

Comparative Example 34

Except that foundation paste F8 was used instead of the foundation pasteE1, a membrane electrode assembly MEA of Comparative Example 34 wasprepared in a manner similar to that of Example 13. It should be notedthat the foundation paste F8 was prepared by mixing 6 g of Teflon(trademark) powder (trade name: L170J, produced by Asahi Glass Co.,Ltd.) and 24 g of carbon black powder (trade name: AB-5, produced byCabot) with ethylene glycol.

Comparative Example 35

Except that the unifying pressure of the decal method in the productionof the membrane electrode assembly CCM was 30 kg/cm², a membraneelectrode assembly MEA of Comparative Example 35 was prepared in amanner similar to that of Example 13.

Comparative Example 36

Except that the unifying pressure of the decal method in the productionof the membrane electrode assembly CCM was 10 kg/cm², a membraneelectrode assembly MEA of Comparative Example 36 was prepared in amanner similar to that of Example 13.

2. Fuel Shortage Test

Fuel shortage tests were performed on fuel cells containing membraneelectrode assemblies of Examples and Comparative Examples mentionedabove. The test conditions were the same as the test of the firstembodiment described above. Differences in voltage calculated byterminal voltages before and after the fuel test are shown in Table 4.TABLE 4 Water Water absorption absorption amount ratio DifferentialPenetration of carbon of anode pressure resistance particles (cc/g)diffusion (mmaq) Adhesion (mΩ) Δ voltage Anode Cathode layer (wt %)Anode Cathode ratio (%) Anode Cathode (mV) Example 13 360 130 65 85 8320 2.2 3.2 28 Example 14 360 80 65 85 83 21 2.2 2.8 24 Example 15 360130 82.4 62 62 19 1.8 2.6 28 Example 16 360 130 50.4 100 105 20 2.6 3.425 Comparative Example 27 360 360 82.4 85 83 21 2.2 3.2 44.7 ComparativeExample 28 360 520 82.4 85 83 22 2.2 2.4 55 Comparative Example 29 130130 37.6 83 83 20 2.6 3.2 32.3 Comparative Example 30 80 130 20 83 83 192.8 3.2 65 Comparative Example 31 360 130 32.2 128 83 19 3.6 3.2 32Comparative Example 32 360 130 95 42 83 21 1.8 3.2 58 ComparativeExample 33 360 130 82.4 85 132 20 2.2 4.8 33.4 Comparative Example 34360 130 82.4 85 45 20 2.2 2.6 62 Comparative Example 35 360 130 82.4 8583 12.5 2.2 3.2 34 Comparative Example 36 360 130 82.4 85 83 7.3 2.2 3.2583. Evaluation

The electrode assemblies of Examples 13 to 16 in which water absorptionamount of carbon particles of the anode diffusion layer and the cathodediffusion layer, water absorption ratio of the anode diffusion layer,differential pressure of the anode diffusion layer and the cathodediffusion layer, and adhesion ratio are within the range of the presentinvention, have penetration resistance of not more than 5 mΩ anddifference of voltage at the fuel shortage test of not more than 30 mV.Efficiencies were not decreased very much. On the other hand, theelectrode assemblies of Comparative Examples 27 and 28 having too highwater absorption amount of carbon particles of the cathode diffusionlayer, the electrode assemblies of Comparative Examples 29 and 30 havingtoo low water absorption amount of the carbon particles of the anodediffusion layer and too low water absorption ratio of the anodediffusion layer, the electrode assembly of Comparative Example 31 havingtoo low water absorption ratio of the anode diffusion layer and too highdifferential pressure of the anode diffusion layer, the electrodeassembly of Comparative Example 32 having too high water absorptionratio of the anode diffusion layer and too low differential pressure ofthe anode diffusion layer, the electrode assembly of Comparative Example33 having too high differential pressure of the cathode diffusion layer,the electrode assembly of Comparative Example 34 having too lowdifferential pressure of the cathode diffusion layer, and the electrodeassemblies of Comparative Examples 35 and 36 having too low adhesionratio, have penetration resistance of not more than 5 mΩ; however,differences in voltages in the fuel shortage tests exceed 30 mV.Efficiencies were decreased very much.

4. Investigation of Contact Angle of Carbon-Based Material

To investigate contact angle of the carbon-based material with water inthe anode diffusion layer and the cathode diffusion layer, electrodeassemblies of Samples 1 to 4 were prepared in a manner similar to thatof Example 13 except for using carbon-based materials each havingdifferent contact angle with water, and fuel shortage tests similar tothose described above was performed. The results are shown in Table 5.

Sample 1

Except that the immersion time in hot water in the hydrophilic treatmentof the carbon paper for the anode diffusion layer was controlled so thatthe contact angle with water was 100°, a membrane electrode assembly MEAof Sample 1 was prepared in a manner similar to that of Example 13.

Sample 2

Except that the immersion time in hot water in the hydrophilic treatmentof the carbon paper for the anode diffusion layer was controlled so thatthe contact angle with water was 130°, a membrane electrode assembly MEAof Sample 2 was prepared in a manner similar to that of Example 13.

Sample 3

Except that the immersion time in hot water in the hydrophilic treatmentof the carbon paper for the cathode diffusion layer was controlled sothat the contact angle with water was 100°, a membrane electrodeassembly MEA of Sample 3 was prepared in a manner similar to that ofExample 13.

Sample 4

Except that the immersion time in hot water in the hydrophilic treatmentof the carbon paper for the cathode diffusion layer was controlled sothat the contact angle with water was 75°, a membrane electrode assemblyMEA of Sample 4 was prepared in a manner similar to that of Example 13.TABLE 5 Water Water absorption absorption amount ratio DifferentialPenetration of carbon of anode pressure resistance particles (cc/g)diffusion (mmaq) Adhesion (mΩ) Δ voltage Anode Cathode layer (wt %)Anode Cathode ratio (%) Anode Cathode (mV) Example 1 75 140 65 85 83 202.2 3.2 28 Sample 1 100 140 82.4 85 83 20 2.2 3.2 36 Sample 2 130 14082.4 85 83 19 2.2 3.2 58 Sample 3 75 100 82.4 85 83 19 2.2 3.2 36.3Sample 4 75 75 82.4 85 83 21 2.2 3.2 54

As is clear from Table 5, in Samples 1 and 2 having larger contact angleof carbon-based material than that of the range of the present invention(that is, water-repellent), water which must be retained in the anodediffusion layer migrates to the anode catalytic layer, and floodingoccurred in the anode catalytic layer, and in Samples 3 and 4 havingsmaller contact angle of carbon-based material than that of the range ofthe present invention (that is, hydrophilic), water generated in thecathode catalytic layer is retained in the cathode, and floodingoccurred in the cathode catalytic layer, and therefore, in spite thepenetration resistance being not more than 5 mΩ, the voltage differencein the fuel shortage test undesirably exceeded 30 mV.

As explained above, by the present invention, the reverse diffusionwater amount from the cathode to the anode can be increased, and waterholding property is given to the anode diffusion layer, not to the anodecatalytic layer. Therefore, water is supplied from the anode diffusionlayer to the anode catalytic layer under conditions of fuel shortage,and the water is electrolyzed in the anode catalytic layer to supplyprotons to the polymer electrolyte membrane. Efficiency deteriorationcan be restrained even under fuel shortage conditions.

1. A membrane electrode assembly for a polymer electrolyte fuel cell,comprising: a polymer electrolyte membrane; and an anode and a cathodeeach having a catalytic layer and a diffusion layer, the anode diffusionlayer further comprising: a carbon-based material; and a water holdinglayer thereon containing water holding material for 5 to 20 wt % oftotal weight of an electron conductive material and the water holdingmaterial, or carbon particles having water absorption amount atsaturated water vapor pressure at 60° C. of not less than 150 cc/g,wherein water absorption ratio of the anode diffusion layer at 60° C. isin a range of 40 to 85%, wherein a differential pressure measured by thedifferential pressure measuring method is in a range of 60 to 120 mmaq,and wherein a ratio of quantity of electric charge of catalytic materialof the cathode catalytic layer existing in proton conductive passagefrom the polymer electrolyte membrane measured by a cyclic voltammetricmethod is not less than 15% of the quantity of electric charge of allthe catalytic material existing in the cathode catalytic layer.
 2. Themembrane electrode assembly for a polymer electrolyte fuel cellaccording to claim 1, wherein the anode diffusion layer comprises: acarbon-based material; a layer thereon having carbon particles andfluorine resin; and a layer thereon having carbon particles, a polymerelectrolyte, void forming agent, and water holding material.
 3. Themembrane electrode assembly for a polymer electrolyte fuel cellaccording to claim 1, wherein the anode diffusion layer comprises: acarbon-based material; a layer thereon having carbon particles, fluorineresin, and water holding material.
 4. A membrane electrode assembly fora polymer electrolyte fuel cell, comprising: a polymer electrolytemembrane; and an anode and a cathode each having a catalytic layer and adiffusion layer, the anode diffusion layer further comprising: acarbon-based material having a contact angle with water of not more than90° by performing a hydrophilic treatment; and a layer thereon havingcarbon particles having water absorption amount at saturated water vaporpressure at 60° C. of not less than 150 cc/g and fluorine resin, whereinwater absorption ratio of the anode diffusion layer at 60° C. is in arange of 40 to 85%, wherein penetration resistance measured by apenetration resistance method is not more than 5 mΩ, wherein adifferential pressure measured by the differential pressure measuringmethod is in a range of 60 to 120 mmaq, and wherein a ratio of quantityof electric charge of catalytic material of the cathode catalytic layerexisting in proton conductive passage from the polymer electrolytemembrane measured by a cyclic voltammetric method is not less than 15%of the quantity of electric charge of all the catalytic materialexisting in the cathode catalytic layer.
 5. A membrane electrodeassembly for a polymer electrolyte fuel cell, comprising: a polymerelectrolyte membrane; and an anode and a cathode each having a catalyticlayer and a diffusion layer, the catalytic layer comprising: at least acatalyst; carbon particles supporting the catalyst; and polymerelectrolyte, the cathode catalytic layer further contains void formingagent, the diffusion layer comprising: a carbon-based material; and alayer thereon containing carbon particles and fluorine resin, whereinwater absorption amount at saturated water vapor pressure at 60° C. ofthe carbon particles of the anode diffusion layer is not less than 150cc/g and water absorption amount at saturated water vapor pressure at60° C. of the carbon particles of the cathode diffusion layer is lessthan 150 cc/g, wherein water absorption ratio of the anode diffusionlayer at 60° C. is in a range of 40 to 85%, wherein a differentialpressure of the anode diffusion layer and the cathode diffusion layermeasured by the differential pressure measuring method is in a range of60 to 120 mmaq and penetration resistance measured by a penetrationresistance method is not more than 5 mΩ, and wherein a ratio of quantityof electric charge of catalytic material of the cathode catalytic layerexisting in proton conductive passage from the polymer electrolytemembrane measured by a cyclic voltammetric method is not less than 15%of the quantity of electric charge of all the catalytic materialexisting in the cathode catalytic layer.
 6. The membrane electrodeassembly for a polymer electrolyte fuel cell according to claim 5,wherein the carbon-based material of the anode diffusion layer hascontact angle with water of not more than 90° by performing ahydrophilic treatment, and the carbon-based material of the cathodediffusion layer has a contact angle with water of not less than 130° byperforming a water-repellent treatment.